The present invention relates to a method of producing high throughput silicon-on-insulator (SOI) materials and, in particular, to a method of fabricating a defect induced buried oxide (DIBOX) region in a semiconductor substrate. The DIBOX region produced by the method of the present invention has improved structural and electrical qualities as compared with prior art BOX regions. Moreover, the method of the present invention produces BOX regions having a fixed charge and a greater thickness than prior art methods. Hence, the method of the present invention saves implant time and ultimately SOI wafer cost.
In semiconductor manufacturing, several processes have been developed to produce a SOI material having a thin buried oxide (BOX) region disposed therein. One such process used in the prior art to produce BOX regions is referred to as SIMOX (separation by implantation of oxygen). In a typical SIMOX process, the BOX region is fabricated by first implanting oxygen using high ion doses (greater than 4xc3x971017 cmxe2x88x922) followed by annealing at high temperatures (greater than 1300xc2x0 C.). Despite the current advances made in this field, most of the prior art SIMOX processes produce a BOX region which is electrically inferior to thermally created oxide regions.
Moreover, prior art low-dose SIMOX processes oftentimes create a BOX region which contains silicon islands buried within the BOX. Typically, BOX regions produced using prior art low-dose SIMOX processes have discrete regions of thicknesses of about 1000 xc3x85 or 2000 xc3x85. These thicknesses are determined by the implanted oxygen dose which is in the range of about 4-5xc3x971017 cmxe2x88x922 for the 1000 xc3x85 thick BOX and about 7-10xc3x971017 cmxe2x88x922 for the 2000 xc3x85 thick BOX. Thinner continuous BOX regions cannot be obtained using prior art SIMOX processes.
Moreover, the prior art uses ion doses to create a BOX region in a semiconductor substrate which makes SIMOX uneconomical and a SIMOX substrate is usually four to six times the bulk-silicon cost. This high cost makes the use of prior art SOI materials undesirable.
In an attempt to reduce the cost of fabricating SOI materials, SIMOX processes using a low dose ion implantation step have been developed. One problem with conventional SIMOX processes using low ion doses is the formation of Si precipitates in the low dose BOX regions. The formation of Si precipitates in the BOX regions is not desirable since it hinders the formation of high quality BOX regions.
Even though BOX quality improves when a room temperature implant follows the base oxygen implant step, Si precipitates are not completely removed. The precipitate density typically increases with increasing base dose. At base doses of greater than 4xc3x971017 cmxe2x88x922 the room temperature oxygen ion implant step produces BOX regions in which the precipitates are distributed throughout the buried oxide region.
In view of the drawbacks mentioned hereinabove concerning prior SIMOX processes, there remains a need for providing a new and improved method of creating a BOX region within SOI materials. Specifically, it would be desirable to provide a new method wherein low dose ion implants can be used without the resultant BOX region having Si precipitates therein.
One object of the present invention is to provide a method of fabricating a semiconductor material containing a defect induced buried oxide (DIBOX) region therein.
Another object of the present invention is to provide a method whereby all of the above-mentioned problems with prior art SIMOX processes have been overcome.
A further object of the present invention is to provide a method which allows for the fabrication of a continuous BOX region using ion doses of about 3xc3x971017 cmxe2x88x922 or less.
A still further object of the present invention is to provide a method which allows for the fabrication of a BOX region that exhibits high structural as well as electrical qualities.
A yet further object of the present invention is to provide a BOX region in a SOI material which has a greater range of thickness than BOX regions prepared using conventional methods.
An even further object of the present invention is to provide a SOI material having a BOX region that contains little or no Si precipitates therein.
An additional object of the present invention is to provide a SOI material having a BOX region in which the charge of the BOX region is fixed to a targeted value.
These as well as other objects and advantages are achieved by the method of the present invention wherein a defect induced buried oxide (DIBOX) region is formed in a semiconductor material by adding to, or replacing oxygen used in the room temperature ion implantation step with another element. The use of other elements in addition to, or besides oxygen in the room temperature ion implant step significantly reduces the Si precipitates in the BOX region.
Specifically, the method of the present invention comprises the steps of:
(a) implanting oxygen ions into a surface of a semiconductor substrate at a base ion dose of about 5xc3x971016 cmxe2x88x922 or above so as to form a stable buried damaged region in said semiconductor substrate;
(b) implanting second ions into said surface of said semiconductor substrate at a second ion dose of about 1xc3x971015 cmxe2x88x922 or above so as to form an amorphous layer adjacent to said stable buried damaged region, wherein said second ions comprise at least one dissimilar ion than said oxygen ions used in step (a);
(c) oxidizing the structure produced by step (b); and
(d) optionally, annealing the oxidized structure provided in step (c).
According to a preferred embodiment of the present invention, step (a) is carried out by implanting oxygen ions into a Si-containing semiconductor substrate, or a preformed SOI substrate which is either bare or contains a cap layer, e.g., a dielectric cap layer, using a low dose ion implantation step which is carried out at a high temperature of about 200xc2x0 C. or greater.
Step (b) of the present invention includes a yet lower ion dose implantation step using the same or different energy range as used in step (a). The second ions employed in step (b) include, but are not limited to: nitrogen, carbon, germanium, bismuth, antimony, phosphorus, arsenic, neon, argon, xenon and mixtures thereof. The second ions may also be mixed, in some embodiments, with oxygen.
Step (b) of the present invention is carried out at about cryogenic temperatures to temperatures of about 300xc2x0 C. or less, with the proviso that the temperature be lower than the oxygen ion implantation step employed in step (a).
This low temperature/low dose ion implantation step, i.e., step (b), may be carried out in either a single step with a single temperature, or multiple steps with multiple temperatures which range from about cryogenic to about 300xc2x0 C. or less may be employed.
The oxidation step, step (c), is typically carried out in an inert ambient such as N2 or Ar mixed with greater than 0.1% oxygen at temperatures of about 1300xc2x0 C. or higher.
The optional step of the present invention is an anneal step which is normally carried out in an ambient containing a mixture of an inert gas and  less than 5% oxygen at temperatures of about 1300xc2x0 C. or higher for a period of time of from about 5 to about 20 hours. The optional anneal step is performed when the foregoing oxidation step does not form a BOX region with desired structural and electrical properties.
The term xe2x80x9chigh structural qualityxe2x80x9d is used herein to denote a structure which has little or no etch pit density (less than about 1xc3x97105 cm2); little or no top or bottom Si/buried oxide roughness (less than about 200 xc3x85 as observed by SEM or TEM); a low HF-defect density (less than about 5 cm2); a low surface roughness (about 6 xc3x85 root mean square(Rms)); and, if present, the silicon precipitates in the buried oxide region at a low density (less than about 1xc3x97105 cm2) and a small size (less than about 500 xc3x85 in height). The structural quality can be determined using optical, atomic force, scanning and/or transmission microscopy.
The term xe2x80x9chigh electrical qualityxe2x80x9d is used herein to denote a structure wherein the BOX breakdown field is high (greater than about 5 megavolts per cm); the BOX minibreakdown voltage is high (greater than about 30 volts); the BOX leakage at a given voltage is low (less than about 1 nanoAmps); and the BOX defect density is low (less than about 2 cm2).
Another aspect of the present invention relates to a SOI material having a continuous BOX region formed in a semiconductor substrate by the method of the present invention. The BOX region formed by the instant invention has a variable, but controllable, continuous thickness which can typically range from about 500 to about 2000 xc3x85 by varying the oxygen ion implantation step such that the base dose is from about 1xc3x971017 to about 6xc3x971017 cmxe2x88x922. Such a controllable, continuous range of BOX thicknesses cannot be obtained utilizing prior art SIMOX processes.
Moreover, the SOI material of the present invention has a BOX region in which the charge thereof is fixed to a targeted value. The fixed charge BOX regions are a result of using different ions during the implantation steps of the present invention.